Method of making inflated metal products



2 Sheets-Sheet 1 E. A. MILLER METHOD OF MAKING INFLATED METAL PRODUCTS March 5, 1968 Filed Aug. 17, 1964 March 5, 1968 E. A. MILLER 3,371,399

METHOD OF MAKING INFLATED METAL PRODUCTS Filed Aug. 17, 1964 2 Sheets-Sheet 2 via-LO United States Patent Ofifice 3,3713% Patented Mar. 5., 1968 3,371,399 METHOD OF MAKING INFLATED METAL PRODUCTS Edwin A. Miiier, Attiehoro, Mass, assignor to Terms Instruments Incorporated, Dallas, Tern, a corporation of Delaware Fiied Aug. 17, 1964, Ser. No. 389,934 13 Ciainrs. (fl. 29-1573) ABSTRACT OF THE DISCLOSURE Among the several objects of the invention may be noted the simplified, low-cost production of improved inflated composite metal products from plates, sheets, strips or the like, said products being of an improved nature ing such products from a Wide variety of metals constituting the starting materials. Other objects and features will e in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the elements and which will .be indicated in the following claims.

In the accompanying drawings, in which several of varone of which is imprinted;

FIG. 2 is a cross section showing one of the strips of FIG. 1 superimposed on the other;

FIG. 3 is a plan view of the superimposed strips of FIG. 2 after a squeezing operation, one of the strips being broken away at the upper left;

FIG. 4 is a cross section taken on line 4-4 of FIG. 3;

FIG. 5 is a view similar to FIG. 3, showing conditions after an inflating step or tubulation;

FIG. 6 is a cross section taken on line 6-6 of FIG. 5

FIG. 7 is a view similar to FIG. 6 but sufiiciently enlarged to illustrate certain bond features; and

FIG. 8 is a view similar to FIG. 7, illustrating an alternative product made according to the invention.

ing parts throughout the several views of the drawings.

Hereinafter the term sheet will be understood to comprehend plates, strips or other areas of metal useful for carrying out the invention.

Inflated products made from bonded sheets are known. However, the bonding heretofore employed has been accomplished by hot-roling of sheets between which a to all areas of stop-off patterns was diflicult, particularl; in cases involving extensive tubulation networks. More over, the strength of the over-all bond between sheets was limited to one which could be separated by inflation in the stopped-off area and there was no possibility of substantially improving such bonds. This disadvantage existed even though holding dies might be used to prevent overall separation of the sheets during inflation.

ing inflation. The products resulting from the invention have a Wider range of application than heretofore, as will appear.

Referring now more particularly to FIG. 1, there are shown at numerals 1 and 3 sheets in the form of strips of any two malleable metals capable of being solid-phase of a metal different from that of the other.

Solid-phase bonding processes such as described in patent 2,691,815 call for careful cleaning of the faces of sheets such as 1 and 3 which are interfacially to be bonded. After such cleaning, and according to the present cases advantageous. Other methods of application besides silk screening are by oifset roll printing, stencil spraying or application of a suitable lacquer followed by dusting While pressing their faces together to establish said green bond according to the patent above-mentioned. For the Reduction occurs in the solid phase of the metal being bonded. The reduction hasthe effect'of green-bonding the strips while elongating or stretching them, in the direction of their lengths. Only inconsequential transverse stretching will occur. It is for this reason that the pattern The result of the above-described reduction by rolling has the effect of green-bonding the entire faces of strips 1 and 3 not occupied by the pattern 5. The final linearly extended configuration of pattern 5 is as shown at 5' in FIG. 3. At the approximate 70% reduction, a ratio of length of shape 5 to shape 5 is about 3.32:1. The resulting green-bonded composite is as shown in FIGS. 3 and 4. This is then coiled and placed in a furnace for sintering, so as to improve the bond strength beyond that of the green bond. For the example under consideration, sintering may be accomplished in a furnace containing an inert protective atmosphere of, for example, nitrogen at i200 F. for two hours. For longer periods in the furnace the temperature may be reduced, for example, as low as 800 F. This in the solid phase converts the comparatively weak green bonds to strong bonds.

After sintering, the bonded composite strip is scrubbed and dried thoroughly and then roll-finished to become flat and straight. The composite strip is then cut into lengths which include the shape 5'. To register the cuts with the pattern 5', holes such as shown at 9 are provided originally in strip 1, properly registered with the foreshortened pattern 5. The cuts are located as shown by the dotted lines 11 in FIG. 3, being taken transversely through the holes 9 in their final positions. Other registering means may of course be employed, such as marginal notches, imprints or the like.

Next the separated individual bonded composite sheets of the example are heated for approximately ten minutes at 1800 F. in a furnace containing an atmosphere of hydrogen constituting a reducing atmosphere. Dissociated ammonia gas may also be used which has a substantial hydrogen content. Such a hydrogen-rich atmosphere is capable of diffusing through most metals, including steel, and in doing so comes into contact with the iron oxide forming the bond-resistant pattern 5. Thus the hydrogen diffuses through SAE 1006 steel and reduces the oxide to form iron, with concomitant release of steam the pressure of which builds up due to its entrapment. The resulting pressure separates or inflates the strips in the area of 5. The amount of inflation depends upon time and temperature and is therefore controllable so that a tubular form may be produced such as shown at 13 in FIGS. 5, 6 and 7. It is preferable that the amount of oxide in the slurry forming the pattern shall be such as to be completely reduced when the desired shape occurs. The reduced iron diffuses into the steel walls within the inflation, thus producing a clean interior in the tubulation, sealed from outside contamination until such time as the product is fabricated into an assembly and appropriate fittings installed for circulating appropriate fluids therethrough. Fitting installation may be accomplished, for example, by cutting along a line such as 15 (FIG. 5) to provide openings in the tubulation 13 for fitting insertion. Obviously fittings may also be installed elsewhere in the tubulation without use of a cut such as 15, or the cut may be taken elsewhere than as shown.

FIG. 7 is an enlargement of FIG. 6, showing by reverse hatching the location of the plane 17 of the final solidphase bond. In practice this bond effected by diffusion during sintering is of such excellent quality that it can hardly be detected microscopically, and its strength approaches that of the metals which are bonded.

In FIG. 8 is shown a variant of the invention in which two sheets 19 and 21 have been processed according to the invention, but in this case sheet 21 is thicker, so that upon inflation by oxide reduction all or substantially all of the deformation occurs in the thinner sheet 19. As a result, instead of having a tubing network which is more or less circular in cross section as shown in FIGS. 6 and 7, it is more or less semicircular in shape, as indicated at 23. As above mentioned, the amount of inflation can readily be controlled by varying the amount of iron oxide contained in the stop-off pattern 5', the time allowed for the hydrogen to diffuse, and the temperature of final i heating employed, the latter controlling the rate of diffusion. Thus, elliptical or semielliptical forms may be produced.

My method of inflation has several advantages, such as the elimination of the use of hydraulic or like equipment, and the absence of manifolding arrangements for inflation, above referred to. Prior manifolding arrangements have also given trouble, in that it has been difficult to inflate an extensive tubular network evenly, due to friction in the flow of inflating liquid. In the case of my invention, pressure is generated evenly at all points in the pattern. Another feature of the invention is that inflation occurs under substantial temperature in the heating furnace for reducing the oxide. At such temperatures the metals of the strongly bonded strips, being inflated in a plastic state, readily respond to pressure to take the final tubular shape. This is not possible in the case of steel, for instance, using oil or other hydraulic fluid. Moreover, no restraining devices are necessary according to the invention, such as often required when hydraulic methods are employed. As above made clear, there is also the advantage of a minimum of contamination, as the iron oxide in the case of steel sheets reduces to iron and becomes part of the tube wall.

While, as above stated, the interior of the finished product is very clean, but being ferrous it may be subject to oxidation when the tube or network 13 is opened and left exposed to moist atmosphere. In order to offset this, zinc oxide or zinc carbonate particles or both may be included with the iron oxide particles of the slurry for imprinting the pattern 5. As a result, the diffusing hydrogen at high temperature will break down the zinc compounds and cause the zinc to diffuse into the steel. The result will be a protective coating on the inside of the tubulation of the finished product which will protect it against corrosion when open. This precaution may not be necessary if the sheets such as 1 or 3 are composed of material less corrodible by moisture, such as aluminum.

The interior surface of the tubulation may be carburized by employing a cellulose binder in the slurry forming the imprint 5. During hot hydrogen diffusion there will be effected a breakdown of such a binder to provide free carbon to form the desired interior carburized coating. For the same purpose an addition of graphite to the oxide slurry may be used. Copper oxide particles may be used instead of, or with the zinc oxides or zinc carbonates above-mentioned, which will result in an interior coating of copper or brass, as the case may be. Other oxides may also be employed, the requirement being that they shall be reducible when heated in the presence of hydrogen and that they are compatible with the metals forming the tubulation to form a coating thereon. The general principle here involved is to provide in the slurry a protective substance suitable for deposition on the inside surface of the tubulation when the hot hydrogen reaches the slurry, and which will protect that surface after deposition. Generally the protective coating diffuses into the metal of the tubulation. This substance may consist of an oxide used for accomplishing the expansion step, as for example copper; or it may be an additive thereto.

It will be understood that the reducing gas need not be made up entirely of hydrogen but like dissociated ammonia should contain enough hydrogen to effect the oxide reduction required.

As above mentioned, the metal composing each of strips 1 and 3 need not be the same and each may be a composite of bonded multilayered metals.

Articles made according to the invention have various uses, such as heat-exchanging walls of refrigerators, warmers and the like. The shape of the pattern is arbitrary and may include that of a network if desired.

It is preferable in order to obtain a tubulation without solid oxides therein that all of the oxide in the material forming the pattern 5 shall be used up in the process of tubulation by chemical reduction to metal and formation of the gaseous product. However in some cases this may not be necessary if convenient means are available for scavenging finished tubulations at the time they are opened for applying fittings.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. The process of making an inflated composite product, comprising applying to at least one of a pair of sheets a stop-off pattern of a substance containing an oxide, interfacially contacting said sheets with the pattern sandwiched therebetween, bonding the interface between the sheets exclusive of said pattern, heating the sheets in a reducing atmosphere penetrable through at least one of the sheets to reduce said oxide and release a gaseous product in the area of the pattern to produce an inflation of at least one of the sheets of a shape determined by said pattern.

2. The process of making an inflated composite metal product, comprising applying to at least one of a pair of clean malleable metal sheets a stop-off pattern of a substance containing a metal oxide, interfacially contacting said sheets with the pattern sandwiched therebetween, squeezing the sheets with physical reduction to produce a solid-phase green-bonded interface therebetween exclusive of said pattern, sintering the green-bonded sheets to improve the interfacial bond, heating the bonded sheets in a reducing atmosphere penetrable through at least one of the sheets to reduce said metal oxide to its metal and release a gaseous product in the area of the pattern to produce an inflation of at least one of the sheets of a shape determined by said pattern.

3. The process of making an inflated composite metal product, comprising applying to at least one of a pair of clean malleable metal sheets a stop-off pattern of a substance containing iron oxide, interfacially contacting said sheets with the pattern sandwiched therebetween, squeezing the sheets with physical reduction to produce a solid-phase green-bonded interface therebetween exclusive of said pattern, sintering the green-bonded sheets to improve the interfacial bond, heating the sheets in a hydrogen-rich atmosphere penetrable through at least one of the sheets to chemically reduce said iron oxide to iron and release a gaseous product in the area of the pattern to produce an inflation of at least one of the sheets of a shape determined by said pattern.

4. The process of making an inflated composite metal product, comprising applying to at least one of a pair of clean malleable ferrous metal sheets a stop-01f pattern of a substance containing oxides of iron and zinc, interfacially contacting said sheets with the pattern sandwiched therebetween, squeezing the sheets with physical reduction to produce a solid-phase green-bonded interface therebetween exclusive of said pattern, sintering the greenbonded sheets to improve the interfacial bond, heating the sheets in a hydrogen-rich atmosphere penetrable through at least one of the sheets to chemically reduce said oxides to their metals and release a gaseous product in the area of the pattern to produce an inflation of at least one of the sheets of a shape determined by said pattern and to diffuse a protective zinc coating on the inner walls of the inflation.

5. The process of making an inflated composite metal product, comprising applying to at least one of a pair of clean malleable ferrous metal sheets a stop-off pattern of a substance containing iron oxide and zinc carbonate, interfacially contacting said sheets with the pattern sandwiched therebetween, squeezing the sheets with physical reduction to produce a solid-phase green-bonded interface therebetween exclusive of said pattern, sintering the green-bonded sheets to improve the interfacial bond, heating the sheets in a hydrogen-rich atmosphere penetrable through at least one of the sheets to chemically reduce said iron oxide and zinc and release a gaseous product in the area of the pattern to produce an inflation of at least one of the sheets of a shape determined by said pattern and to diffuse a protective zinc coating on the inner walls of the inflation.

6. The process of making an inflated composite metal product, comprising applying to at least one of a pair of clean malleable ferrous metal sheets a stop-01f pattern of a substance containing iron oxide and graphite, interfacially contacting said sheets with the pattern sandwiched therebetween, squeezing the sheets with physical reduction to produce a solid-phase green-bonded interface therebetween exclusive of said pattern, sintering the green-bonded sheets to improve the interfacial bond, heating the strips in a hydrogen-rich atmosphere penetrable through at least one of the sheets to chemically reduce said iron oxide and release a gaseous product in the area of the pattern to produce an inflation of at least one of the sheets of a shape determined by said pattern and to carburize the inner walls of the inflation.

7. The process of making an inflated composite metal product, comprising applying to at least one of a pair of clean malleable ferrous metal sheets a stop-olf pattern of a substance containing iron oxide and cellulose, interfacially contacting said sheets with the pattern sandwiched therebetween, squeezing the sheets with physical reduction toproduce a solid-phase green-bonded interface therebetween exclusive of said pattern, sintering the greenbonded sheets to improve the interfacial bond, heating the sheets in a hydrogen-rich atmosphere penetrable through at least one of the sheets to chemically reduce said iron oxide and release a gaseous product in the area of the pattern to produce an inflation of at least one of the sheets of a shape determined by said pattern and t0 carburize the inner walls of the inflation.

8. The process of making an inflated composite metal product, comprising applying a stop-off pattern of a substance containing an oxide to at least one of a pair of clean malleable metal sheets, interfacially contacting said sheets with the pattern sandwiched therebetween, squeezing the sheets to reduce their total thickness to produce a solid-phase green bond therebetween, sintering the green-bonded sheets to improve the bond, heating the strips in a reducing atmosphere which will penetrate at least one of the sheets and reduce said oxide and form an expansive medium in the pattern thereby to produce an inflation of at least one of the sheets of a shape substantially that of said pattern.

9. The process according to claim 8, wherein said substance of the stop-off pattern includes iron oxide and wherein said reducing atmosphere contains hydrogen.

It The process according to claim 9, wherein said substance of the stop-off pattern further also includes an oxide of a metal which is corrosion-resistant to water to diffuse into the inner surfaces of the inflation.

11. The process of making inflated composite metal products, com-prising applying to at least one of two clean malleable metal strips a stop-off pattern foreshortened in the direction of the length of the strip to which it is applied, interfacially contacting said strips with the pattern sandwiched therebetween, passing the strips lengthwise between rolls to squeeze them with a physical reduction for green-bonding them in the solid state and thereby linearly extending said pattern, sintering the green-bonded strips to improve the bond, heating the sintered and bonded strips in a reducing atmosphere which will penetrate at least one of the metal strips and reduce said oxide to its subsisting metal and to form a gaseous medium in the confines of the pattern, to inflate at least one of the strips in a shape determined by said pattern.

12. The process of making inflated composite metal products, comprising applying a stop-01f pattern of a substance containing a metal oxide to at least one of a pair of clean malleable metal sheets, interfacially contacting said sheets With the pattern sandwiched therebetween, squeezing the sheets with a physical reduction to produce a solid-phase green bond therebetween exclusive of said pattern, sintering the green-bonded sheets to improve the interfacial bond, heating the strips in a hydrogen-rich atmosphere which Will penetrate at least one of the sheets and chemically reduce its oxide and form a gaseous medium in the pattern to produce an inflation of at least one of the sheets of a shape substantially that of said pattern.

13. The process of making an inflated composite metal product, comprising applying to at least one of a pair of clean malleable metal sheets a stop-oh. pattern of a substance containing an oxide and a compatible protective material for at least one of the metal sheets, interfacially contacting said sheets with the pattern sandwiched therebetween, squeezing the sheets with physical reduction to produce a solid-phase green-bonded interface between the sheets exclusive of said pattern, sintering the green-bonded sheets to improve the interfacial bond, heating the sheets in a hydrogen-rich atmosphere penetrable through at least one of the sheets chemically to reduce .said oxide and release products from the oxide and protective material in the area of the pattern to produce an inflation of at least one of the sheets of a shape determined by said pattern and to dilfuse a protective coating on inner wall parts of the inflation.

References Cited UNITED STATES PATENTS 2,593,460 4/1952 Johnson.

2,691,815 10/1954 Boessenkool et 211.

2,766,514 10/1956 Adams 29l57.3 2,990,608 7/1961 Manning 29157.3 3,015,157 1/1962 Reynolds et al 29470.9 3,019,513 2/1962 Hornaday et al. 291573 3,061,924 11/1962 Brick et a1. 29470.9 3,166,837 1/1965 Prick et a1. 29421 3,271,846 9/1966 Buechele et a1 29-l57.3

JOHN F. CAMPBELL, Primary Examiner.

I. D. HOBART, Assistant Examiner. 

